Organic thin film transistor, method of fabricating the same, and display device including the same

ABSTRACT

An organic thin film transistor (OTFT) includes an organic semiconductor layer on a substrate, source/drain electrodes spaced apart from each other on the substrate, a mixed layer between the source/drain electrodes and the organic semiconductor layer, the mixed layer including an organic material and a metal oxide or metal salt, and a gate electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to an organic thin filmtransistor (OTFT), a method of fabricating the same, and a displaydevice including the same. More particularly, embodiments of the presentinvention relate to an OTFT having enhanced hole/electron injectionproperties.

2. Description of the Related Art

In general, organic thin film transistors (OTFTs) refer to thin filmtransistors having an organic layer as a semiconductor layer instead ofa silicon layer. The organic semiconductor layer may include a lowmolecular weight organic compound, e.g., oligothiophene, pentacene, andso forth, or a polymer, e.g., polythiophene, and so forth.

The conventional OTFT may operate, e.g., as a driving device of adisplay device. When the OTFT is employed in a conventional displaydevice, the display device may include at least two OTFTs, e.g., aswitching OTFT and a driving OTFT, a capacitor, a plurality ofelectrodes and a light source on a substrate, e.g., a flexiblesubstrate. The conventional OTFT may include a gate electrode,source/drain electrodes, a gate insulating layer between the gateelectrode and the source/drain electrodes, and an organic semiconductorlayer on the source/drain electrodes.

However, disposing the organic semiconductor layer directly on thesource/drain electrodes may increase a resistance therebetween, i.e.,impede formation of an ohmic contact, due to differences in Fermienergies of the organic semiconductor layer and the source/drainelectrodes. For example, manufacturing at low temperatures, e.g., due tothermal sensitivity of a plastic flexible substrate, may limit a dopingconcentration in the organic semiconductor layer, consequently causing areduced flow of holes/electrons between the source/drain electrodes andthe organic semiconductor layer due to a high resistance therebetween.Accordingly, there exists a need for an OTFT having a reduced resistancebetween the organic semiconductor layer and the source/drain electrodesin order to enhance hole/electron injection properties therebetween.

SUMMARY OF THE INVENTION

Embodiments of the present invention are therefore directed to anorganic thin film transistor (OTFT), a method of fabricating the same,and a display device including the same, which substantially overcomeone or more of the disadvantages of the related art.

It is therefore a feature of an embodiment of the present invention toprovide an OTFT having a structure capable of reducing resistancebetween the organic semiconductor layer and the source/drain electrodes.

It is therefore another feature of an embodiment of the presentinvention to provide a display device including an OTFT with enhancedholes/electrons injection properties.

It is yet another feature of an embodiment of the present invention toprovide a method of fabricating an OTFT having a structure capable ofreducing resistance between the organic semiconductor layer and thesource/drain electrodes.

At least one of the above and other features and advantages of thepresent invention may be realized by providing an OTFT including asubstrate, a gate electrode disposed on the substrate, a gate insulatinglayer disposed on the entire surface of the substrate including the gateelectrode, source and drain electrodes spaced apart from each other onsome regions of the gate insulating layer, a mixed layer disposed on thesource and drain electrodes and including an organic material and ametal oxide, and a P-type organic semiconductor layer disposed on thesubstrate including the mixed layer.

The organic semiconductor layer may be a P-type organic semiconductorlayer. Accordingly, the organic material of the mixed layer may be atriarylamine-based material or an acene-based material. The acene-basedmaterial may be anthracene, tetracene, pentacene, perylene, or coronene.The metal oxide may be molybdenum oxide (MoO₃), vanadium oxide (V₂O₅),tungsten oxide (WO₃) or nickel oxide (NiO). The metal oxide may bepresent in the mixed layer at an amount of about 25% to about 80% basedon a total weight of the mixed layer.

At least one of the above and other features and advantages of thepresent invention may be also realized by providing an OTFT including asubstrate, a gate electrode disposed on the substrate, a gate insulatinglayer disposed on the entire surface of the substrate including the gateelectrode, source and drain electrodes spaced apart from each other onsome regions of the gate insulating layer, a mixed layer disposed on thesource and drain electrodes and including an organic material and ametal salt, and an N-type organic semiconductor layer disposed on thesubstrate including the mixed layer.

The organic semiconductor layer may be a N-type organic semiconductorlayer. Accordingly, the organic material of the mixed layer may becomprised of a material selected from the group consisting of acene,fully fluorinated acene, partially fluorinated acene, partiallyfluorinated oligothiophene, fullerene, fullerene having substituent,fully fluorinated phthalocyanine, partially fluorinated phthalocyanine,perylene tetracarboxylic diimide, perylene tetracarboxylic dianhydride,naphthalene tetracarboxylic diimide, and naphthalene tetracarboxylicdianhydride. The acene-based material may be anthracene, tetracene,pentacene, perylene, coronene, or a fluorinated acene. The metal saltmay contain an alkali metal or an alkaline-earth metal. The metal saltmay be cesium chloride (CsCl), cesium fluoride (CsF) or cesium carbonate(Cs₂CO₃). The amount of the metal salt in the mixed layer may be about5% to about 50% based on a total weight of the mixed layer.

At least one of the above and other features and advantages of thepresent invention may be also realized by providing a light emittingdisplay device including a substrate, a gate electrode disposed on thesubstrate, a gate insulating layer disposed on the entire surface of thesubstrate including the gate electrode, source and drain electrodesspaced apart from each other on some regions of the gate insulatinglayer, a mixed layer disposed on the source and drain electrodes, andincluding an organic material and a metal oxide, a P-type organicsemiconductor layer disposed on the substrate including the mixed layer,a passivation layer disposed on the P-type organic semiconductor layer,a first electrode connected to the source and drain electrodes, a pixeldefining layer exposing a portion of the first electrode, an organiclayer disposed on the first electrode, and including an organic emittinglayer, and a second electrode disposed on the organic layer.

At least one of the above and other features and advantages of thepresent invention may be also realized by providing a light emittingdisplay device including a substrate, a gate electrode disposed on thesubstrate, a gate insulating layer disposed on the entire surface of thesubstrate including the gate electrode, source and drain electrodesspaced apart from each other on some regions of the gate insulatinglayer, a mixed layer disposed on the source and drain electrodes, andincluding an organic material and a metal salt, an N-type organicsemiconductor layer disposed on the substrate including the mixed layer,a passivation layer disposed on the N-type organic semiconductor layer,a first electrode connected to the source and drain electrodes, a pixeldefining layer exposing a portion of the first electrode, an organiclayer disposed on the first electrode, and including an organic emittinglayer, and a second electrode disposed on the organic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent to those of ordinary skill in the art bydescribing in detail exemplary embodiments thereof with reference to theattached drawings, in which:

FIG. 1 illustrates a cross-sectional view of an organic thin filmtransistor (OTFT) according to an exemplary embodiment of the presentinvention;

FIG. 2 illustrates a cross-sectional view of an OTFT according toanother exemplary embodiment of the present invention;

FIG. 3 illustrates a cross-sectional view of a display device includingan OTFT according to an exemplary embodiment of the present invention;and

FIG. 4 illustrates a cross-sectional view of a display device includingan OTFT according to another exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Korean Patent Application Nos. 10-2006-111182 and 10-2006-111183, bothfiled on Nov. 10, 2006, in the Korean Intellectual Property Office, andentitled: “Organic Thin Film Transistor, Method of Fabricating the Same,and Organic Light Emitting Display Device Including the Same,” areincorporated by reference herein in their entirety.

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are illustrated. The invention may, however, beembodied in different forms and should not be construed as limited tothe embodiments set forth herein. Rather, these embodiments are providedso that this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

In the figures, the dimensions of layers and regions may be exaggeratedfor clarity of illustration. It will also be understood that when alayer or element is referred to as being “on” another layer orsubstrate, it can be directly on the other layer or substrate, orintervening layers may also be present. Further, it will be understoodthat when a layer is referred to as being “under” another layer, it canbe directly under, and one or more intervening layers may also bepresent. In addition, it will also be understood that when a layer isreferred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent. Like reference numerals refer to like elements throughout.

An exemplary embodiment of an organic thin film transistor (OTFT)according to the present invention will now be described more fully withreference to FIG. 1. As illustrated in FIG. 1, an OTFT may include asubstrate 200, a gate electrode 210, a gate insulating layer 220 on thesubstrate 200, source/drain electrodes 230, an organic semiconductorlayer 250, and a mixed layer 240 between the organic semiconductor layer250 and the source/drain electrodes 230.

The substrate 200 of the OTFT according to an embodiment of the presentinvention may be formed of a transparent material, e.g., glass, tofacilitate transmission of ultraviolet (UV) light therethrough.Alternatively, the substrate 200 may be formed of silicon or plastic,e.g., polyethersulphone (PES), polyacrylate, polyetherimide,polyethylene naphthalate (PEN), polyethylene terephthalate (PET),polyphenylene sulfide (PPS), polyarylate, polyimide, polycarbonate (PC),cellulose tri acetate (TAC), cellulose acetate propionate (CAP), and soforth.

The gate electrode 210 of the OTFT according to an embodiment of thepresent invention may be formed of a conductive material, e.g., analuminum (Al), an Al-alloy, molybdenum (Mo), a Mo-alloy, and so forth.

The gate insulating layer 220 of the OTFT according to an embodiment ofthe present invention may be formed on the substrate 200 and incommunication with the gate electrode 210, such that the gate electrode210 may be positioned between the substrate 200 and the gate insulatinglayer 220, as illustrated in FIG. 1. The gate insulating layer 220 maybe formed of a single layer, e.g., a single organic insulating layer ora single inorganic insulating layer, a multi-layer structure, e.g., aplurality of organic insulating layers or a plurality of inorganicinsulating layers, or an organic-inorganic hybrid structure. Aninorganic material employed in the gate insulating layer 220 mayinclude, e.g., silicon oxide (SiOx), silicon nitride (SiNx), aluminumoxide (Al2O3), tantalum oxide (Ta2O5), barium strontium titanate (BST),lead zirconium titanate (PZT), and so forth. An organic materialemployed in the gate insulating layer 220 may include polyacryl, e.g.,polymethyl methacrylate (PMMA), polystyrene (PS), a phenol-basedpolymer, a polyimide, a polyaryl-ether, a polyamide, a fluorine-basedpolymer, a p-xylene-based polymer, a polyvinylalcohol-based polymer,parylene, and so forth.

The source/drain electrodes 230 of the OTFT according to an embodimentof the present invention may be spaced apart from each other on the gateinsulating layer 220. The source/drain electrodes 230 may include asingle metal layer, e.g., aluminum (Al), silver (Ag), molybdenum (Mo),gold (Au), platinum (Pt), palladium (Pd), nickel (Ni), indium-tin-oxide(ITO), indium-zinc-oxide (IZO), or an alloy thereof. Alternatively, thesource/drain electrodes 230 may be formed of a plurality of metal layersincluding at least one adhesion metal layer, e.g., titanium (Ti),chromium (Cr), aluminum (Al), and so forth.

The organic semiconductor layer 250 of the OTFT according to anembodiment of the present invention may be formed on the substrate 200.More specifically, the organic semiconductor layer 250 may be formed asa P-type organic semiconductor layer or as a N-type organicsemiconductor layer on the entire surface of the substrate 200 in orderto cover the mixed layer 240, as will be discussed in detail below.Alternatively, P-type or N-type impurities may be doped only intosource/drain regions of the OTFT.

When the organic semiconductor layer 250 is a P-type organicsemiconductor layer, it may include an acene-based compound, e.g.,pentacene, perylene, tetracene, anthracene, perylene, coronene, and soforth, poly-thienylenevinylene, poly-3-hexylthiophene, α-hexathienylene,naphthalene, α-6-thiophene, α-4-thiophene, rubrene, polythiophene,polyparaphenylenevinylene, polyparaphenylene, polyfluorene,polythiophenevinylene, polythiophene-heterocyclic aromatic copolymer,triarylamine, and derivatives thereof. Alternatively, when the organicsemiconductor layer 250 is an N-type organic semiconductor layer, it mayinclude an acene-based compound, a fully fluorinated acene, a partiallyfluorinated acene, a partially fluorinated oligothiophene, afullerene-based compound, a fluorinated phthalocyanine, e.g., a fullyfluorinated phthalocyanine and a partially fluorinated phthalocyanine,perylene tetracarboxylic diimide, perylene tetracarboxylic dianhydride,naphthalene tetracarboxylic diimide, and naphthalene tetracarboxylicdianhydride.

The mixed layer 240 of the OTFT according to an embodiment of thepresent invention may be formed on the source/drain electrodes 230 byco-deposition to a thickness of about 10 angstroms to about 1000angstroms. A thickness of the mixed layer 240 below about 10 angstromsmay be insufficient to enhance hole/electron injection efficiency, and athickness above about 1000 angstroms may unnecessarily increase costsand process time. The mixed layer 240 may be disposed between theorganic semiconductor layer 250 and the source/drain electrodes 230 tominimize or eliminate contact therebetween.

Without intending to be bound by theory, it is believed that disposingthe mixed layer 240 between the organic semiconductor layer 250 and thesource/drain electrodes 230 may position the mixed layer 240 between ahighest occupied molecular orbital (HOMO) level of the organicsemiconductor layer 250 and a HOMO level of the source/drain electrodes230 to minimize resistance therebetween. In other words, even though anumerical difference between the Fermi level of the source/drainelectrodes 230 and the HOMO level of the organic semiconductor layer 250may provide a large value that is unchanged with respect to aconventional OTFT having no mixed layer, a HOMO level of the mixed layer240 positioned between the source/drain electrodes 230 and the organicsemiconductor layer 250 may minimize the large value, i.e., energydifference between the Fermi level of the source/drain electrodes 230and the HOMO level of the organic semiconductor layer 250. The reducedenergy difference may reduce overall resistance between the source/drainelectrodes 230 and the organic semiconductor layer 250, consequentlyincreasing transport of holes or electrons into the P-type or N-typeorganic semiconductor layer 250, respectively, through the mixed layer240.

The mixed layer 240 may be formed of a mixture containing an organicmaterial and a metal oxide or metal salt. More specifically, thecomposition of the mixed layer 240 may be determined with respect to amaterial employed to form the organic semiconductor layer 250, i.e.,whether the organic semiconductor layer 250 is formed as a P-typeorganic semiconductor layer or as a N-type organic semiconductor layer.In detail, if the organic semiconductor layer 250 is formed as a P-typelayer, the mixed layer 240 may include a P-type organic compound and ametal oxide. Alternatively, if the organic semiconductor layer 250 isformed as a N-type layer, the mixed layer 240 may include a N-typeorganic compound and a metal salt.

In further detail, when the organic semiconductor layer 250 is formed asa P-type semiconductor layer, the mixed layer 240 may include a metaloxide, e.g., molybdenum oxide (MoO₃), vanadium oxide (V₂O₅), tungstenoxide (WO₃), nickel oxide (NiO), and so forth, in an amount of about 25%to about 80% by weight of the mixed layer 240. If the amount of metaloxide is below about 25% by weight of the mixed layer 240, resistancebetween the source/drain electrodes 230 and the organic semiconductorlayer 250 may be reduced insufficiently. On the other hand, if theamount of metal oxide is above about 80% by weight of the mixed layer240, a surface roughness of the mixed layer 240 may be too high, therebyreducing reliability of the OTFT. The P-type organic material employedin the mixed layer 240 may be any type of material capable oftransporting organic charges. The P-type organic material may beidentical to the P-type organic material employed to form the organicsemiconductor layer 250, e.g., an acene-based material or a materialcontaining triarylamine.

When the organic semiconductor layer 250 is formed as a N-typesemiconductor layer, the mixed layer 240 may include a metal salt, e.g.,cesium chloride (CsCl), cesium fluoride (CsF), cesium carbonate(Cs₂CO₃), and so forth, in an amount of about 5% to about 50% by weightof the mixed layer 240. The metal salt may include an alkali metal or analkaline earth metal. If the amount of metal salt is below about 5% byweight of the mixed layer 240, resistance between the source/drainelectrodes 230 and the organic semiconductor layer 250 may be reducedinsufficiently. On the other hand, if the amount of metal salt is aboveabout 50% by weight of the mixed layer 240, electron injectionefficiency may be lower as compared to a comparable mixed layer, i.e., alayer having a substantially similar composition, including no metalsalt. The N-type organic material employed in the mixed layer 240 may beidentical to the N-type organic material employed to form the organicsemiconductor layer 250.

According to another exemplary embodiment of an OTFT illustrated in FIG.2, the OTFT may include a substrate 300, source/drain electrodes 330 onthe substrate 300, an organic semiconductor layer 350 on the substrate300, a mixed layer 340 between the organic semiconductor layer 350 andthe source/drain electrodes 330, a gate electrode 310 on the organicsemiconductor layer 350, and a gate insulating layer 320 between theorganic semiconductor layer 350 and the gate electrode 310. Thecomposition and structure of the elements of the OTFT described withrespect to FIG. 2 are identical to the composition and structure ofrespective elements of the OTFT described previously with respect toFIG. 1, with the exception of forming the gate electrode 310 on theorganic semiconductor layer 350, and accordingly, their detaileddescription will not be repeated herein. In this respect, it should benoted that first digits of reference numerals, i.e., ‘2’ and ‘3’, areemployed to distinguish embodiments and not elements, and therefore,reference numerals having identical last two digits refer to similarelements.

According to yet another exemplary embodiment of the present invention,a display device, e.g., an organic light emitting display device, may beformed to include the OTFT described previously with respect to FIG. 1.The flat display device may include, as illustrated in FIG. 3, an OTFT,a passivation layer 460 on the OTFT, a pixel defining layer 475, firstand second electrodes 470 and 490 on the passivation layer 460, and alight emitting layer 480 between the first and second electrodes 470 and490. The OTFT may include a substrate 400, a gate electrode 410, a gateinsulating layer 420, source/drain electrodes 430, a mixed layer 440,and an organic semiconductor layer 450.

More specifically, the substrate 400 may be prepared, and the gateelectrode 410 may be formed thereon. The gate insulating layer 420 maybe deposited to cover the entire surface of the substrate 400 includingthe gate electrode 410. The source/drain electrodes 430 may be spacedapart from each other on the gate insulating layer 420. The mixed layer440 may be formed on the source/drain electrodes 423 by a co-depositionmethod. The organic semiconductor layer 450 may be formed on the entiresurface of the substrate 400 including the mixed layer 440, such thatthe mixed layer 440 may be positioned between the source/drainelectrodes 430 and the organic semiconductor layer 450 to minimize or toprevent contact therebetween, to complete formation of the OTFTillustrated in FIG. 3. The OTFT employed in the display device describedwith respect to FIG. 3 may be similar to the OTFT described previouslywith respect to FIG. 1, and therefore, detailed description of itsrespective elements will not be repeated herein. In this respect, itshould be noted that first digits of reference numerals, i.e., ‘2’ and‘4’, are employed to distinguish embodiments and not elements, andtherefore, reference numerals having identical last two digits refer tosimilar elements.

The passivation layer 460 of the display device according to anembodiment of the present invention may be deposited on the substrate400 above the OTFT. The passivation layer 460 may be formed on theentire surface of the substrate including the organic semiconductorlayer 450 of SiNx, SiOx, or a multiple layer thereof. If the displaydevice is a top light emitting display device, a planarization layer(not shown) may be deposited on the passivation layer 460. An uppersurface of the passivation layer 460 may be etched to form a via hole460 a therethrough in order to expose an upper surface of thesource/drain electrode 430.

The first electrode 470 of the flat panel display according to anembodiment of the present invention may be formed on the passivationlayer 460 and in communication with the source/drain electrode 430 ofthe OTFT through the via hole 460 a. The first electrode 470 may beformed of a transparent conductive material having a low work function,e.g., ITO and IZO. The first electrode 470 may also include at least onereflective layer of a non-transparent metal, e.g., Al, Ag, or an alloythereof, below the conductive material in order to reflect emitted lightin an upward direction.

The pixel defining layer 475 of the display device according to anembodiment of the present invention may be deposited and patterned onthe first electrode 470 to form an opening 475 a to expose an uppersurface of the first electrode 470. The pixel defining layer 475 may beformed of benzo-cyclobutene, polyimide, polyamide, acrylic resin,silicon-on-glass (SOG), and like materials.

The light emitting layer 480 of the display device according to anembodiment of the present invention may be formed on the first electrode470 of a light emitting material, e.g., organic light emitting material,by inkjet printing, deposition, laser-induced thermal imaging, and soforth. The organic layer 480 may have a single layer structure or amulti-layer structure, e.g., a hole injection layer, a hole transportlayer, an electron injection layer, an electron transport layer, and/ora hole blocking layer.

The second electrode 490 of the display device according to anembodiment of the present invention may be formed on the entire surfaceof the substrate 400 including the organic layer 480. The secondelectrode 490 may be formed of silver (Ag), aluminum (Al), calcium (Ca),magnesium (Mg), or an alloy thereof.

According to still another exemplary embodiment of the presentinvention, a display device, e.g., an organic light emitting displaydevice, may be formed to include the OTFT described previously withrespect to FIG. 2. The display device may include, as illustrated inFIG. 4, an OTFT, a passivation layer 560 on the OTFT, a pixel defininglayer 575, first and second electrodes 570 and 590 on the passivationlayer 560, and a light emitting layer 480 between the first and secondelectrodes 570 and 590. The OTFT may include a substrate 500, a gateelectrode 510, a gate insulating layer 520, source/drain electrodes 530,a mixed layer 540, and an organic semiconductor layer 550. The displaydevice in FIG. 4 may be similar to the display device describedpreviously with respect FIG. 3, with the exception of including the OTFTdescribed previously with respect to FIG. 2. Accordingly, detaileddescription of the OTFT respective elements will not be repeated herein.In this respect, it should be noted that first digits of referencenumerals, i.e., ‘3’ and ‘5’, are employed to distinguish embodiments andnot elements, and therefore, reference numerals having identical lasttwo digits refer to similar elements.

According to embodiments of the present invention, a mixed layer of anorganic material and a metal-containing material, i.e., a metal oxide ora metal salt, between an organic semiconductor layer and source/drainelectrodes may reduce resistance therebetween, so that hole or electronmobility may be enhanced between an organic semiconductor layer andsource/drain electrodes, thereby facilitating fabrication of a flatpanel display device with improved image quality.

Exemplary embodiments of the present invention have been disclosedherein, and although specific terms are employed, they are used and areto be interpreted in a generic and descriptive sense only and not forpurposes of limitation. Accordingly, it will be understood by thoseskilled in the art that various changes in form and details may be madewithout departing from the spirit or scope of the present invention asset forth in the following claims.

1. An organic thin film transistor (OTFT), comprising: a substrate; agate electrode disposed on the substrate; a gate insulating layerdisposed on the entire surface of the substrate including the gateelectrode; source and drain electrodes spaced apart from each other onsome regions of the gate insulating layer; a mixed layer disposed on thesource and drain electrodes and including an organic material and ametal oxide; and a P-type organic semiconductor layer disposed on thesubstrate including the mixed layer.
 2. The OTFT according to claim 1,wherein the organic material includes a material containing triarylamineor an acene-based material.
 3. The OTFT according to claim 1, whereinthe metal oxide is molybdenum oxide (MoO₃), vanadium oxide (V₂O₅),tungsten oxide (WO₃), or nickel oxide (NiO).
 4. The OTFT according toclaim 1, wherein the mixed layer has a thickness of about 10 Å to about1000 Å.
 5. The OTFT according to claim 1, wherein the mixed layercontains about 25 wt % to about 80 wt % metal oxide based on a totalweight of the mixed layer.
 6. The OTFT according to claim 2, wherein theacene-based material is one of anthracene, tetracene, pentacene,perylene, and coronene.
 7. An organic thin film transistor (OTFT),comprising: a substrate; a gate electrode disposed on the substrate; agate insulating layer disposed on the entire surface of the substrateincluding the gate electrode; source and drain electrodes spaced apartfrom each other on some regions of the gate insulating layer; a mixedlayer disposed on the source and drain electrodes and including anorganic material and a metal salt; and an N-type organic semiconductorlayer disposed on the substrate including the mixed layer.
 8. The OTFTaccording to claim 7, wherein the organic material comprises a materialselected from the group consisting of acene, fully fluorinated acene,partially fluorinated acene, partially fluorinated oligothiophene,fullerene, fullerene having substituent, fully fluorinatedphthalocyanine, partially fluorinated phthalocyanine, perylenetetracarboxylic diimide, perylene tetracarboxylic dianhydride,naphthalene tetracarboxylic diimide, and naphthalene tetracarboxylicdianhydride.
 9. The OTFT according to claim 7, wherein the metal saltcontains an alkali metal or an alkaline-earth metal.
 10. The OTFTaccording to claim 7, wherein the mixed layer has a thickness of about10 angstroms to about 1000 angstroms.
 11. The OTFT according to claim 7,wherein the mixed layer contains about 5 wt % to about 50 wt % metalsalt based on a total weight of the mixed layer.
 12. The OTFT accordingto claim 8, wherein the acene-based material is one of anthracene,tetracene, pentacene, perylene, and coronene.
 13. The OTFT according toclaim 9, wherein the metal salt is cesium chloride (CsCl), cesiumfluoride (CsF), or cesium carbonate (Cs₂CO₃).
 14. A light emittingdisplay device, comprising: a substrate; a gate electrode disposed onthe substrate; a gate insulating layer disposed on the entire surface ofthe substrate including the gate electrode; source and drain electrodesspaced apart from each other on some regions of the gate insulatinglayer; a mixed layer disposed on the source and drain electrodes, andincluding an organic material and a metal oxide; a P-type organicsemiconductor layer disposed on the substrate including the mixed layer;a passivation layer disposed on the P-type organic semiconductor layer;a first electrode connected to the source and drain electrodes; a pixeldefining layer exposing a portion of the first electrode; an organiclayer disposed on the first electrode, and including an organic emittinglayer; and a second electrode disposed on the organic layer.
 15. Thelight emitting display device according to claim 14, wherein the organicmaterial includes a material containing triarylamine or an acene-basedmaterial.
 16. The light emitting display device according to claim 14,wherein the metal oxide is molybdenum oxide (MoO₃), vanadium oxide(V₂O₅), tungsten oxide (WO₃), or nickel oxide (NiO).
 17. The lightemitting display device according to claim 14, wherein the mixed layerhas a thickness of about 10 angstroms to about 1000 angstroms.
 18. Thelight emitting display device according to claim 14, wherein the mixedlayer contains about 25 wt % to about 80 wt % metal oxide based on atotal weight of the mixed layer.
 19. A light emitting display device,comprising: a substrate; a gate electrode disposed on the substrate; agate insulating layer disposed on the entire surface of the substrateincluding the gate electrode; source and drain electrodes spaced apartfrom each other on some regions of the gate insulating layer; a mixedlayer disposed on the source and drain electrodes, and including anorganic material and a metal salt; an N-type organic semiconductor layerdisposed on the substrate including the mixed layer; a passivation layerdisposed on the N-type organic semiconductor layer; a first electrodeconnected to the source and drain electrodes; a pixel defining layerexposing a portion of the first electrode; an organic layer disposed onthe first electrode, and including an organic emitting layer; and asecond electrode disposed on the organic layer.
 20. The light emittingdisplay device according to claim 19, wherein the organic materialcomprises a material selected from the group consisting of acene, fullyfluorinated acene, partially fluorinated acene, partially fluorinatedoligothiophene, fullerene, fullerene having substituent, fullyfluorinated phthalocyanine, partially fluorinated phthalocyanine,perylene tetracarboxylic diimide, perylene tetracarboxylic dianhydride,naphthalene tetracarboxylic diimide, and naphthalene tetracarboxylicdianhydride.
 21. The light emitting display device according to claim19, wherein the metal salt contains an alkali metal or an alkaline-earthmetal.
 22. The light emitting display device according to claim 19,wherein the mixed layer has a thickness of about 10 angstroms to about1000 angstroms.
 23. The light emitting display device according to claim19, wherein the mixed layer contains about 5 wt % to about 50 wt % metalsalt based on a total weight of the mixed layer.
 24. The light emittingdisplay device according to claim 21, wherein the metal salt is cesiumchloride (CsCl), cesium fluoride (CsF), or cesium carbonate (Cs₂CO₃).